This invention relates to the production of a zero valent metal from an aqueous solution containing a metal salt. More particularly, this invention relates to the production of a zero valent metal from an aqueous solution containing a salt of a metal wherein the metal salt has a reduction potential of at least about +0.5 V or greater.
Heretofore, zero valent metals have been recovered from solutions of their salts in one of several ways. Such metals have frequently been recovered using ion exchange resins whereby the metal salts of the solution are bound to functional groups which exist on a polymeric backbone and thereby concentrated. This ion exchange treatment has generally been followed by combustion of the resin whereby the metal is recovered directly as a result of the combustion or is recovered by electrochemical or chemical deposition of the metal eluted from its bound position on the ion exchange resin.
Zero valent metals have also been recovered directly from a solution of a metal salt by an electrochemical exchange reaction between the dissolved metal salt and a more electropositive zero valent base metal.
An additional method for recovering zero valent metal from its solution involves chemical treatment of the metal salt to precipitate an insoluble salt or complex which is then followed by further treatment such as combustion, reduction of the metal salt by chemical or electrolytic means, or by hydrogenation.
The processes set forth above suffer from the disadvantage that they all involve multistep sequences, with the economic disadvantages attendant to such multisteps, and, in some instances, such processes are pH dependent and often employ expensive regenerants. Additionally, not all of the processes set forth above obtain the zero valent metal in a relatively pure state and require additional complex refining steps.
The Journal of the Chemical Society, Chemical Communications, No. 12, pages 489 and 490, T. C. Clarke, et al (June 14, 1978) is directed to the production of doped polyacetylene film to give a high electrically conducting polyacetylene and modification of the conductivity of such polyacetylene by treatment with Lewis bases. The journal article sets forth that polyacetylene film, when exposed to silver perchlorate or silver tetrafluoroborate in toluene, results in the doping of polyacetylene film and the production of free silver. However, the production of free silver is incidental to the main purpose, i.e. the doping of polyacetylene film. When polyacetylene film is doped, the doping of the polyacetylene film will reduce, to some extent, the capacity of the polyacetylene to reduce the metal salt to a zero valent metal. Therefore, the use of a doped polyacetylene film to reduce a metal salt to the zero valent metal is less efficacious then the use of a polyacetylene which is not doped.
It is an object of this invention, therefore, to provide a process for the production of zero valent metals from a solution of salts of the desired metal.
Another object of this invention is to provide a process to separate one or more metals from an aqueous solution of the salts of the several metals dissolved in said solution.
Other objects and advantages will become apparent from the following more complete description and claims.